Rupert Grint (It's Only a Play), Keke Palmer (Cinderella) and Ben Platt (The Book of Mormon) are first-timers on Broadway, but not first-timers to fame.

Rupert Grint
Photo by Joan Marcus

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On Aug. 24, Rupert Grint turned 26 — he celebrated at the Bathtub Gin, a Victorian-inspired speakeasy in Chelsea. Two days later, Keke Palmer turned 21 — her mother threw her a surprise birthday party at a beach house. The next month, on Sept. 24, Ben Platt also turned 21 — he rang in the milestone with friends at a "big party" in downtown NYC.

Their birthday celebrations are standard for twentysomethings in the Big Apple. However, unlike most young adults their age, the three also celebrate film success, superstardom and their first time on Broadway.

"I'm getting very spoiled," admitted Platt, who rose to fame as nerdy illusionist Benji Applebaum in the 2012 musical film "Pitch Perfect," and who currently stars as Elder Cunningham in the megahit musical The Book of Mormon. "A quiet audience for us is like a great audience for every other show. It's a blessing to be a part of something that's so strong."

Since "Pitch Perfect," Platt's career has skyrocketed. He was cast in the Chicago production of Mormon (before transferring to Broadway, making his debut), asked back for the "Perfect" sequel and tapped for "Ricki and the Flash," a new film starring Meryl Streep. When he steps outside the Eugene O'Neill stage door, he confessed, "Sometimes I'm overwhelmed."

Singer, actress and television host Palmer, a former Nickelodeon kid, was overcome with emotion as she bowed for the first time in the title role of Cinderella —making her the first African-American Ella to grace the Great White Way.

"I felt the true magic of Broadway," she said from her dressing room at the Broadway Theatre. With only a half-hour to places, she talked into the mirror as her hair was pinned to become a princess — but her smile could be seen from anywhere within her royal quarters.

She explained, "When you're in it, and when you're living things, a lot of times it's hard for you to realize what you've done. I've been in the industry for 11 or 12 years, and it's just so crazy because I'm only 21. When I go out [of the stage door], people say, 'I watched you grow up.' It's kind of unbelievable to me, but it's a good feeling to have them out there because I feel like they're all my family."

Keke Palmer
Photo by Carol Rosegg

Wunderkind "Harry Potter" star Grint, who happens to play a "wunderkind director" in It's Only a Play, said the same.

"The fans have grown up with all of us," he explained. "There's a real loyalty with them, and they support us in whatever we do, and I see a lot of familiar faces at the stage door, which is really nice to know that they're still on our side. It's quite scary doing these things outside the ten years of 'Potter.'"

He confessed that when "Harry Potter" had come to an end, "It was quite a life-changing moment. It dawned on me that this was all over, and it had been such a huge constant part of my life." Suddenly, he said, it made him think, "What am I going to do now?"

Finding fame at such a young age put pressure on each.

"I feel a lot of pressure, but I feel a lot of my pressure is on myself — wanting to make sure that I do my best," said Palmer. Expectations are high. In Platt's case, his father is a well-known producer — and a force behind Broadway's long-running Wicked.

"There's definitely pros and cons," said Platt of his father Marc Platt (If/Then, "Into the Woods"). "It's mostly a wonderful thing because my dad has a lot of experience and can be a great guy in terms of vision making. Because I grew up with him always working, I have been around the entertainment business, so I kind of know how it works… The tough part is a lot of people will assume things. That's part of the reason that my dad and I have tried really hard to not work on the same things. We kept our careers very separate, and I've always earned everything that I've gotten. This is the first time that we'll be on the same project."

Ben Platt
Photo by Joan Marcus

The new project for the Platts is "Ricki and Flash," in which Ben will play a local bartender who worships Streep's character. The elder Platt serves as a producer. Ben was cast after director Jonathan Demme saw him in Mormon. "I feel very confident going in, but of course I'm going to be shaking in my boots next to Meryl Streep," he admitted.

Although they've conquered the worlds of film, fame and (now) Broadway, they each look ahead to their future. Grint is determined to step outside of his comfort zone; Palmer is focusing on her music and a book; and Platt has the option to attend Columbia University (he deferred enrollment when performing took off).

"We're the generation that made all these things that once weren't possible possible," said Palmer. "There's a revolution that's going to happen. That's who our generation is… We question everything, and that's the beautiful thing about us — we question so much that we're able to really figure out the answers to everything. I'm happy to be alive right now — to be my age."

(This feature appears in the November issue of Playbill magazine. Playbill.com staff writer Michael Gioia's work appears in the news, feature and video sections of Playbill.com as well as in the pages of Playbill magazine. Follow him on Twitter at @PlaybillMichael.)